This invention relates generally to signal processors of the type wherein signal components which encompass a broad frequency spectrum can be simultaneously analyzed.
Compressive signal processors provide the same general function as do more conventional spectrum analyzers except that they operate at a much faster rate. For example, a compressive processor can analyze a 100 MHz spectrum to a frequency resolution of 140 KHz within 20 microseconds. By comparison a standard spectrum analyzer would require 10,000 microseconds to accomplish this task.
Prior art compressive processors are described in the article by Warren White entitled "Rapid Frequency Scan" in the February 1960 edition of the Proceedings of the IRE, at page 4A; and in the article by R. L. Goodwin, and F. J. Mueller entitled "A High Sensitivity Parametric Receiver Using Pulse Compression Techniques" presented at the IRE Professional Group on Military Electronics Symposium held in Los Angeles, Calif., February 1962.
One such previous technique for the design of compressive processors involves processing the applied signals through a mixer which also responds to a linear frequency versus time waveform type signal that is provided by a sweeping local oscillator circuit. The output signal from the mixer is processed through a linear FM (frequency modulation) type dispersive delay line. The linear frequency modulation on the output signal from the mixer is removed by the dispersive delay line which has a linear frequency versus time transfer characteristic with a slope equal in magnitude but opposite in polarity from the slope of the output signal of the sweeping local oscillator. The output signal from the dispersive delay line is comprised of a series of pulses which are displaced in time as a function of the frequency of the corresponding portions of the applied signals and whose amplitudes are representative of the relative energy content of the applied signals.
Although the above described dispersive delay line type of compressive processor is most satisfactory for many applications, the processor's scanning rate is limited to a single value which is set by the characteristics of the dispersive delay line; and for this type of processor to operate at multiple scan rates it must incorporate as many dispersive delay lines as there are scanning rates. The just mentioned limitation is particularly restrictive, for example, in applications which involve a large frequency range which must be rapidly scanned to monitor for signals having time durations from one microsecond to CW (continuous wave); and wherein once signals have been detected using the fast scan rate, different scans at slower rates and reduced frequency coverage are needed to resolve signals of multiple contiguous frequencies.